"Ultramarathons are an up and coming sport where participants run for multiple days straight, covering hundreds of kilometers, climbing up to 40 m high over the terrain. At first glance, this might sound like an excruciating way to tear up your body all weekend, but results from a study showed that participants were taxing their bodies up to 30% less at the 200 mile mark than at the 100. Exhaustion plays a big role in this. Participants that went the full distance were about 4 minutes per mile slower than their counterparts who did half the distance. It appears that “slow and steady” really does have advantages in a race setting."
... see http://www.popularmechanics.com/science/health/breakthroughs/when-running-200-miles-is-easier-on-your-body-than-running-100-15632972
